With reference to the state of the art, the following printed publications are cited:
(1) U.S. Pat. No. 4,778,834 PA0 (2) WO-A 94/23944 PA0 (3) Antonucci, J. M., Dent. Mat. 7: 124-129, 1991 PA0 (4) EP 0 193 588 B1 PA0 (5) EP 0 625 490 A1 PA0 (6) DE 39 32 469 C2 PA0 (7) DE 23 26 100 B2 PA0 (8) DE 25 01 683 A1 PA0 (9) U.S. Pat. No. 5,304,577 PA0 (10) Derwent Abstract No. 85-021799 04! PA0 (11) Derwent Abstract No. 85-022140 04!. PA0 one mixed apatite of type A1), PA0 two mixed apatites of type A1), PA0 three mixed apatites of type A1), PA0 one mixed apatite of type A2), PA0 two mixed apatites of type A2), PA0 three mixed apatites of type A2), PA0 one mixed apatite of type A3), PA0 two mixed apatites of type A3), PA0 three mixed apatites of type A3), PA0 one mixed apatite of type A1) and one mixed apatite of type A2), PA0 one mixed apatite of type A1) and one mixed apatite of type A3), PA0 one mixed apatite of type A2) and one mixed apatite of type A3), PA0 one mixed apatite of type A1) and two mixed apatites of type A2), PA0 one mixed apatite of type A1) and two mixed apatites of type A3), PA0 one mixed apatite of type A2) and two mixed apatites of type A3) PA0 two mixed apatites of type A2) and one mixed apatite of type A3), PA0 two mixed apatites of type A1) and one mixed apatite of type A2), PA0 two mixed apatites of type A1) and one mixed apatite of type A3), or PA0 one mixed apatite of type A1), one mixed apatite of type A2) and one mixed apatite of type A3).
Publication (1) describes dental materials that are produced by the combination of hydroxylapatite, Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2, in concentrations of up to 70% with polymerisable monomers. Prior to being mixed in, the hydroxylapatite particles are coated with a silicate covering and are silanised in the conventional manner for dental materials. Disadvantageous aspects of these materials are that the ion exchange (calcium, phosphate) with the environment is extensively restricted by the silicate covering and that no transparency such as is required of dental filling materials can be achieved in the material, since at 1.625 the refractive index of hydroxylapatite, Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2, is too high in comparison with the polymeric components. This results in opaque materials having only low transmission of light, as a result of which the photopolymerisation of these materials is possible only in very thin layers. Furthermore, the material is not capable of releasing fluoride ions, which are desirable in particular for dental materials, since they can act to prevent caries.
Publication (2) describes dental materials that are produced by the combinations of sintered fluorapatite, Ca.sub.10 (PO.sub.4).sub.6 F.sub.2, in concentrations between 10 and 70 per cent by volume with polymerisable monomers. Although these dental materials are able to release the desired fluoride ions into their environment, they are unable to satisfy the present-day requirements as regards the translucence of dental materials, since at 1.63 the refractive index of fluorapatite, Ca.sub.10 (PO.sub.4).sub.6 F.sub.2, is too high in comparison with the polymeric components employed. This likewise results in opaque materials having only low transmission of light.
With a view to overcoming this deficiency, publication (3) proposes the use of calcium metaphosphates, Ca (PO.sub.3).sub.2 !.sub.n, as a result of which a reduction in the refractive index to 1.54-1.59 can be achieved. Although dental materials having the desired transparency can be produced with these fillers, in comparison with fluorapatite this filler possesses a higher solubility and does not have the capacity to emit fluoride.
Therefore, with a view to the production of dental filling materials having the requisite transparency, fillers are desirable which exhibit the low solubility and the emission of fluoride as exhibited by fluorapatite but which have a refractive index lying within the range of that of the calcium metaphosphates.
In publication (4), means that contain carbon apatite and the use of carbon apatite for implants are described. However, the phosphate/carbonate apatites disclosed lack a toothlike transparency and also a strength such as is required for the region subject to masticatory pressure in the case of tooth fillings. By reason of its high opacity, the material does not cure under the action of light but is self-curing and consequently can only be used for the implant field.
Although phosphate apatites containing carbonate that are obtainable in accordance with the process of publication (5) have greater porosity and translucence, the refractive index is still inadequate. In combination with acrylates, an opaque material would result.
Antimicrobial hydroxylapatite powders are known from publication (6).
Publication (7) describes, as does publication (8), bioactive composite materials for prosthetic purposes, in particular two-phase glasses with a crystalline apatite phase embedded in a glass phase. However, with the conventional acrylate resins such materials inevitably result in cloudiness. In particular, phosphate apatites with low proportions of carbonate are described which, as is generally known, do not exhibit the required optical properties. Since the disclosed glass phase is also not opaque to X-rays, no tooth-filling materials are to be expected from the described glass-phase/apatite/acrylate combinations.
Publication (9) relates exclusively to phosphate apatites. Strontium phosphate apatite has, as does calcium phosphate apatite, a refractive index of 1.63. The problem of lowering the refractive index cannot be solved by exchanging calcium for strontium. The authors therefore aim for application in the non-visible region (cements for bone defects, tooth root, periodontium). All in all, under the conditions described, only dental materials having high opacity and insufficient strength for fillings in the visible region which is subject to masticatory pressure are obtained.
Publications (10) and (11) describe pure phosphate apatites. In combination with the named dimethacrylates, opaque pastes result. Their opacity is also discernible in that they cannot be cured with light pertaining to the visible spectrum (too little depth of penetration of the light), but rather the initiator system (amine/peroxide) has to be distributed in a two-paste material that can only be activated by mixing. Since apatite is used exclusively by way of filler, the strength of the resulting materials is too low. The stated cation substitutions and also the substitutions for X result in no reduction in the refractive index.